1. Field of the Invention
The present invention relates to an image pickup apparatus equipped with a function that combines image data of a plural images obtained by consecutive photographing to generate combined image data of a single image, and to an image processing method.
2. Description of the Related Art
In recent years, image pickup apparatuses have been proposed that are equipped with a function that combines a plurality of images obtained by consecutive photographing to thereby generate a single image. The image combination in this case is performed for the purpose of, for example, generating a high dynamic range image (HDR image), a low noise image (NR (noise reduction) image), or a super-resolution image. With respect to the plurality of images that are the source of the image combination, it is desirable that there is little camera shake during exposure and that an amount of a positional shift between each image is small.
On the other hand, image stabilization mechanisms (IS mechanisms) that correct camera shake by moving an image pickup device or a lens have also been proposed.
With regard to camera shake during exposure, the camera shake during exposure can be corrected if the image stabilization mechanism is used during exposure of each image at a time of consecutive photographing. Further, with regard to a positional shift between respective images, for example, in Japanese Patent Application Laid-Open Publication No. 2006-86741, technology is disclosed that efficiently corrects a positional shift between respective images by determining an image stabilization range based on information such as a pixel pitch, a focal length, and angular blur between images obtained by blur detecting means.
In this case, when an IS mechanism is continuously operated while a plurality of images are been consecutively photographed, in some cases the stroke limit of the IS mechanism will be exceeded. In such a case, it is not possible to correct camera shake during exposure. Therefore, in order to correct camera shake during exposure of each image with the same accuracy, centering processing is performed that returns the IS mechanism to the initial position thereof each time photographing of a single image ends. However, the centering processing produces a positional shift between the respective images.
With respect to the above described positional shift between images, it is possible to calculate a global vector showing a shift amount by performing a correlation operation between images, and to correct the positional shift during combination processing based on the calculated global vector. For example, in Japanese Patent Application Laid-Open Publication No. 2012-49603, technology is described that compares two images to acquire a local vector showing a partial shift amount, acquires a global vector showing a shift amount for the entire images, and aligns and combines the two images using these acquired vectors.
However, in particular, in a case where the exposure time will be long or the like, because the stroke amount of the IS mechanism is increased and the positional shift amount between images caused by centering processing also increases, a considerably wide region will be adopted as a search target for calculating a global vector that shows a shift amount based on the images. In addition, when the positional shift between images is large, it means that an image portion that is common to a plurality of images is small.
In this connection, conventionally, in a camera in which an IS mechanism is mounted, in order to confirm the photographing range immediately prior to photographing without being affected by camera shake, the IS mechanism is actuated from a time point at which a first release switch is turned on, and thereafter when a second release switch is turned on, the actual exposure is performed while continuing to perform image stabilization while the IS mechanism remains in an actuated state. By this means, in particular in a case where camera shake is liable to arise, such as telephotography, confirmation of a photographing range can be stably performed.